In traditional machines with striking mechanisms a piston which pneumatically or hydraulically is made to move back and forth in a propulsion chamber is used, where the piston strikes directly or indirectly via for example a drill steel shank against the end of a drilling steel which in turn bears on the rock via a drill bit. The stress pulse provides forces at the contact with the rock that makes the rock break.
Efforts have been made with rock breaking machines which contrary to the traditional machines with striking mechanisms have a piston that does not move as far back and forth in the propulsion chamber for transfer of the impact force which brings about a possibility to increase the impact frequency.
WO 2005/002801 shows a striking device such as a rock drill, where a stress pulse is generated in a tool by means of the striking device by that pressure fluid is fed to the striking device and is fed out from the striking device. The pressure fluid that is fed to the striking device is pulsed to a working chamber in the striking device.
If one in a device of the above mentioned type wants to adapt the energy in the stress pulse which is generated in a tool to that which is required to work the rock, one can vary the level of the pressure which is fed to the striking device. However, the pump and the hoses limit the range within which the pressure can be varied.